1. Field of the Invention
The present invention relates to an accumulator which is used as a pressure accumulator or a pulsation pressure damping device. The accumulator according to the present invention is used, for example, in a hydraulic system for a motor vehicle or a hydraulic system for an industrial equipment.
2. Description of the Conventional Art
Conventionally, as shown in FIG. 10, there has been known an accumulator 51 structured such that an accumulator housing 52 is provided with a gas filling port 54 as well as being provided with an oil port 53 which is connected to a pressure piping (not shown), an internal space of the accumulator housing 52 is sectioned into a gas chamber 57 filling the gas, and a fluid chamber 58 communicating with the oil port 53, by a bellows 55 and a bellows cap 56, and the accumulator 51 is activated to accumulate pressure and damp pulsation pressure on the basis of movement of the bellows cap 56, and extension and contraction of the bellows 55 so that gas pressure and liquid pressure balance (refer to Japanese Unexamined Patent Publication No. 2003-172301).
Further, the accumulator 51 is provided with a safety mechanism (a safety mechanism for a pressure decreasing time) 59 which prevents the bellows 55 from being damaged due to the unbalance between the gas pressure and the liquid pressure in the case that the pressure of the fluid chamber 58 is decreased together with the pressure decrease of the pressure piping. In other words, in the case that the pressure of the pressure piping is extremely decreased due to the operation stop of the equipment, the liquid (oil) is discharged little by little from the oil port 53, the bellows 55 is contracted little by little by the filled gas pressure according to the liquid discharge, and a seal 60 provided in a lower surface of the bellows cap 56 comes into contact with an end surface of a stay 61 so as to form a so-called zero-down state. The stay 61 is a metal molded part in which a liquid entrance port 61c is provided in an end surface portion 61b in a leading end of a tubular portion 61a. In the zero-down state, a part of the liquid is trapped within the fluid chamber 58 by the seal 60, and the pressure of the trapped liquid and the gas pressure of the gas chamber 57 are balanced. Therefore, the bellows 55 is inhibited from being damaged due to an excess stress applied to the bellows 55.
Further, the accumulator 51 is provided with a safety mechanism (an emergency safety mechanism) 62 which prevents the liquid within the fluid chamber and the gas within the gas chamber 57 from rapidly expanding in an emergency such as a fire occurrence and prevents the accumulator 51 from exploding. In other words, in the case that the liquid within the fluid chamber 58 and the gas within the gas chamber 57 rapidly expanding due to the fire occurrence, a rupture disc (a weak portion) 61d provided in a part on a circumference of a peripheral surface (the tubular portion 61a) of the stay 61 bursts due to the high pressure, and the high pressure is released from the burst portion. Therefore, it is possible to inhibit an internal portion of the accumulator 51 from coming to an extremely high pressure and exploding.
However, in the prior art mentioned above, since the emergency safety mechanism 62 is constructed by the rupture disc 61d which is provided in the part on the circumference of the peripheral surface (the tube portion 61a) of the stay as mentioned above, the burst pressure becomes higher (such a great pressure as to burst the metal plate is necessary). As a result, there is a disadvantage that the emergency safety mechanism 62 is not activated until the extremely high pressure is established. Further, in order to form the rupture disc 61d in the part on the circumference of the peripheral surface (the tubular portion 61a) of the stay 61, it is necessary to press the stay 61 and thereafter additionally execute a cutting work. Therefore, there is a disadvantage that it take a lot of man hour and time to manufacture the stay 61.